[also known as "pay-it-forward." Instead of paying back a kindness, a person can pay forward the kindness.] I want to say thank you to those who always help English learners on italki to correct their grammar. Your selfless dedication has created a good learning environment here. If one day, my English is as good as yours, I will help those English learners just like what you have done. I think this is the so-called “Make contribution to the society”.